Article In Brief
Investigators injected transgenic Alzheimer's disease mice with tissue from human cadaveric pituitary growth hormone and found that the amyloid-beta deposits were able to infect, “seed,” and lay down clumps of amyloid-beta. The finding suggest that these decades-old samples can transmit one of the pathological hallmarks of Alzheimer's disease.
Some human cadaveric pituitary growth hormone (c-hGH) samples used from the 1950s through the mid-1980s to treat children with short stature were contaminated with prion protein, which decades later resulted in Creutzfeldt–Jakob disease (CJD).
On autopsy, scientists also found amyloid-beta protein (Abeta) deposits in the blood vessels and in between neurons, hints of a pathology that could have ultimately led to Alzheimer's disease (AD).
Now, three years after their first report of the Abeta deposits, scientists at the MRC Prion Unit of University College London in collaboration with scientists at Brigham & Women's Hospital and Harvard Medical School, collected c-hGH samples stored since 1985 (when companies substituted synthetic pituitary growth hormone) and found that the Abeta deposits were able to infect, “seed,” and lay down clumps of Abeta in transgenic AD animal models.
The findings, published December 13 in Nature, suggest that these decades-old samples can transmit one of the pathological hallmarks of AD.
While human-derived pituitary growth hormone is no longer used, the finding raises concern that Abeta material can still set in motion an active toxic state, and the possibility that microscopic Abeta deposits may be resistant to normal cleansing of surgical tools in the neurosurgery suite and could ultimately pose a risk for people undergoing brain surgery.
Rare cases of prion infectivity have been linked to medical or surgical procedures. More than 200 individuals treated with c-hGH worldwide have died of iatrogenic CJD, according to John Collinge, MD, professor of neurology and head of the MRC Prion Unit and senior author of the new study.
Dr. Collinge and his team have been involved with a long-term prospective study of prion disease.
Study Methods, Findings
The findings from the groups' initial 2015 paper in Nature led them to the idea that the stored batches of c-hGH may provide insights into why Abeta was found in the blood vessels and in parts of the brain tissue in people who underwent hormone treatment in childhood and died of prion disease decades later.
“This was unexpected and out of proportion for what you would expect to see in patients in their 30s and 40s,” Dr. Collinge explained. “They had no other risk factors. We thought that the human growth hormone batches may have been seeded with amyloid-beta.”
Public Health England had archived vials of c-hGH, and the scientists were able to obtain samples of some of the material linked back to the eight patients in their earlier study who had died of prion disease. The small amounts of dried powder had been sitting in vials on shelves for more than 30 years.
The 2015 Nature paper reported that the scientists had identified Abeta pathology in the brain tissue and cerebral blood vessels of seven of eight CJD patients tested.
There were several manufacturing procedures used at the time, and only one of them, Hartree-modified Wilhelmi procedure (HWP), has been linked to contaminated material that led to prion disease. Dr. Collinge said that every CJD patient received at least one injection of this hormone preparation as a child.
Now, as reported in the current study, the scientists were able to identify the vials used during the treatments and to distinguish those that were manufactured with other procedures. The material was sent to Dominic M. Walsh, PhD, associate professor at Brigham & Women's Hospital and Harvard Medical School. Dr. Walsh and his team were blinded to the preparations in the vials.
Study Methodology, Findings
To conduct the seeding studies, the research team injected small amounts of the material into the brains of transgenic mice expressing a mutant humanized amyloid precursor protein (APP). As a control, they also injected synthetic pituitary hormone into other transgenic animals
They analyzed the vials for the presence of Abeta peptides (Abeta1–40 and Abeta1–42) and tau proteins. All of the HWP vials tested were positive for Abeta1–40 and tau, and all but one was also positive for Abeta1–42, said Dr. Collinge. They could not detect Abeta peptides or tau in hormone vials manufactured with other preparation methods.
They found that the stored c-hGH material (processed with the HWP technique) seeded and spread Abeta pathology. Abeta seeding did not take place in animals who received the hormone prepared with other non-HWP techniques.
They also injected the decades-old material into wild-type mice that express only murine APP and saw no amyloid deposition, just as they had expected.
“I was amazed that we could seed the material,” said Dr. Collinge.
“Indeed, it is remarkable that detectable seeding activity has persisted at all after decades of storage,” he and his colleagues wrote in the paper. “Our proposal that human transmission of Aβ pathology had occurred as a result of intramuscular injection of c-hGH is now firmly supported by experimental evidence.”
The scientists said they are now conducting studies to see whether the tau identified in the c-hGH vials can seed aggregation in transgenic mice expressing human tau protein.
Others have conducted studies showing it is possible to transmit AD pathology, Dr. Collinge said. “Although we are generating evidence that AD pathology is transmissible, there is no suggestion that AD itself or cerebral amyloid angiopathy or CJD is contagious,” he added. “You can't catch these diseases by contact.”
There has also been no evidence of iatrogenic spread of AD, although the evidence from this study suggests that those patients with evidence of Abeta pathology might have ultimately developed clinical signs of Alzheimer's had they lived longer.
Some of the patients with amyloid aggregation in their cerebral blood vessels had enough pathology to meet a diagnosis of CAA. The Abeta pathology did not meet the full pathological criteria of Alzheimer's disease, according to Dr. Collinge.
“This material may have been contaminated with Abeta seeds and prions,” he added.
“Although we reiterate that there is no suggestion that Alzheimer's disease is contagious, and no supportive evidence from epidemiological studies that it is transmissible (notably by blood transfusion), we consider it important to evaluate the risks of iatrogenic transmission of CAA, and potentially of Alzheimer's disease,” the scientists wrote in the paper.
“Given the lack of disease-modifying therapeutics for Alzheimer's disease and other distressing and fatal neurodegenerative conditions, it will be important to consider introducing improved methods for removing proteopathic seeds from surgical instruments on a precautionary basis.”
“The finding solidifies that the amyloid-beta pathology found in the patients who died of CJD was transmitted by human material,” said David M. Holtzman, MD, FAAN, the Andrew B. and Gretchen P. Jones professor and chairman of the department of neurology at Washington University School of Medicine. “This practice of using human pituitary growth hormone doesn't occur anymore. While they proved that this material transmits amyloid pathology, none of the CJD patients developed clinical manifestations of Alzheimer's disease. It could be that they didn't live long enough. Whether any of this is currently relevant we just don't know.”
Dr. Holtzman co-authored an editorial on the study in the same issue of Nature. “But some people wonder whether people undergoing brain surgery could be at risk from direct contact with contaminated material left behind on tools,” he told Neurology Today. “The field should explore whether this material is resistant to sterilization and could be left behind on instruments used during brain surgery.”
“Scenarios such as this are all still very rare but we still worry mostly because of issue of transmissibility,” said Samuel E. Gandy, MD, PhD, professor of neurology and psychiatry and the Mount Sinai chair in Alzheimer's disease research at the Icahn School of Medicine at Mount Sinai. “For example, I am a dementia expert but I have seen only two CJD patients in my life, so it's really rare, but if you're the one patient who has CJD, it's 100 percent fatal for you.”
“Another issue is incubation time,” he continued. “At this point, we are nearly 35 years past the peak of pituitary extract use. Between 1963 and 1985, about 7,700 children in the United States and 27,000 children worldwide were given growth hormone extracted from human pituitary glands. This would mean that children treated between 1985 and the current day will have outgrown the need for hormone and hopefully they will have outgrown the window of opportunity for prion disease to appear.”
“The Alzheimer transmissibility risk used to be believed to be zero but there is evidence from our work and others that while AD is far less transmissible than CJD, AD transmission potential may be greater than zero,” Dr. Gandy pointed out. There has also been concern about CJD contamination of the blood supply.
Dr. Gandy cited research by a team of scientists in Germany, France, and Spain that characterized the presence and distribution of CJD agents (sporadic and variant forms) in the blood. They quantified the levels of infectivity associated with different blood fractions from CJD affected patients. The blood cells (white and red blood cells) and the plasma from a variant CJD affected patient contained infectivity, he said. Regarding sporadic CJD, infectivity was detected in the plasma of two out of the four investigated cases.
There are no blood tests to identify misfolded brain proteins associated with Alzheimer's, Parkinson's. and prion disease, Dr. Gandy noted. But he added that federal scientists at the Rocky Mountain Laboratories in Montana, part of the National Institutes of Health, are testing ultrasensitive RT-QuIC seed amplification assays for disease-associated tau, alpha-synuclein, and prion aggregates in cerebrospinal fluid.
“They recently described a tau RT-QuIC prototype to diagnosis and confirmation of Pick's disease (with predominant 3R tau pathology) in postmortem CSF samples,” Dr. Gandy said.
Drs. Collinge and Gandy reported no relevant disclosures. Dr. Holtzman has served on the scientific advisory board or consulted for Genentech, Eli Lilly, and AbbVie.